--- a/Modules/_io/stringio.c	Wed Jul 22 02:32:34 2009 +0000
+++ b/Modules/_io/stringio.c	Wed Jul 22 03:07:33 2009 +0000
@@ -550,22 +550,42 @@
 {
     char *kwlist[] = {"initial_value", "newline", NULL};
     PyObject *value = NULL;
+    PyObject *newline_obj = NULL;
     char *newline = "\n";
 
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|Oz:__init__", kwlist,
-                                     &value, &newline))
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OO:__init__", kwlist,
+                                     &value, &newline_obj))
         return -1;
 
+    /* Parse the newline argument. This used to be done with the 'z'
+       specifier, however this allowed any object with the buffer interface to
+       be converted. Thus we have to parse it manually since we only want to
+       allow unicode objects or None. */
+    if (newline_obj == Py_None) {
+        newline = NULL;
+    }
+    else if (newline_obj) {
+        if (!PyUnicode_Check(newline_obj)) {
+            PyErr_Format(PyExc_TypeError,
+                         "newline must be str or None, not %.200s",
+                         Py_TYPE(newline_obj)->tp_name);
+            return -1;
+        }
+        newline = _PyUnicode_AsString(newline_obj);
+        if (newline == NULL)
+            return -1;
+    }
+
     if (newline && newline[0] != '\0'
         && !(newline[0] == '\n' && newline[1] == '\0')
         && !(newline[0] == '\r' && newline[1] == '\0')
         && !(newline[0] == '\r' && newline[1] == '\n' && newline[2] == '\0')) {
         PyErr_Format(PyExc_ValueError,
-                     "illegal newline value: %s", newline);
+                     "illegal newline value: %R", newline_obj);
         return -1;
     }
     if (value && value != Py_None && !PyUnicode_Check(value)) {
-        PyErr_Format(PyExc_ValueError,
+        PyErr_Format(PyExc_TypeError,
                      "initial_value must be str or None, not %.200s",
                      Py_TYPE(value)->tp_name);
         return -1;
@@ -577,6 +597,9 @@
     Py_CLEAR(self->writenl);
     Py_CLEAR(self->decoder);
 
+    assert((newline != NULL && newline_obj != Py_None) ||
+           (newline == NULL && newline_obj == Py_None));
+
     if (newline) {
         self->readnl = PyUnicode_FromString(newline);
         if (self->readnl == NULL)